1. Be laid back and friendly, smile a lot, show you're having fun. People like positive people. Thank people for their help/time. This goes a LONG way.
2. Show interest in the material at hand. One of the cool things about path is that we are all constantly learning. You should have some kind of intellectual curiosity, or at least the good sense to act like you are there to learn. If someone suggests a learning opportunity for you, for God's sake, take them up on it.
3. Don't be overly political and/or aggressive. It's cool to arrange a meeting or two with the bigwigs (chair, PD) but there's nothing more obnoxious than a student who kisses ass to the attendings and blows off the residents. You'll spend the majority of your time with your fellow residents, not attendings, so it pays to get to know them. Plus, they often have a say in the ranklist!
4. Don't ask a million questions about your application, your chances of matching there, etc. It only makes you look neurotic, and is annoying. But do ask questions about the program. It's a good time to find out whether you would really want to end up there for a minimum of 4 years.